Europe's most well-known extinct humans, the Neanderthals, probably evolved their distinctive facial features in a chaotic "Game of Thrones" manner, as their ancestors clashed and competed in a harsh Ice Age environment, researchers say.

A study of 17 fragmented skulls pulled from an underground karst in northern Spain shows that archaic Europeans bore a surprising diversity of facial features roughly 430,000 years ago, according to researchers.

In a study published Thursday in the journal Science, authors argued that this variation proved Neanderthals did not evolve their projecting noses, powerful jaws and protruding teeth in a long, gradual process.

Instead, these traits — and others — began cropping up among different groups of ancestors at different times in a process called accretion.

At a news conference Thursday, lead study author Juan-Luis Arsuaga, a professor of paleontology at the Complutense University of Madrid, compared the process to the book and television series "Game of Thrones."

"As in the famous saga, there was never a unified and uniform middle Pleistocene kingdom, but a number of houses living in different regions and often competing for the land," Arsuaga said.

Each house, he said, consisted of an extended family, and these extended families were either closely, or distantly, related to other groups. These houses would have lost and gained territory as glaciers advanced and retreated over the continent, sometimes separating groups and sometimes herding them together.

"According to this scenario, hominid evolution was not a peaceful and boring process of very slow change across an immense land," Arsuaga said. "There was not simply one kind of hominin living in that big territory."

The skull fragments were among the remains of 28 individuals uncovered at the Sima de los Huesos, or "Pit of Bones," cave in Sierra de Atapuerca.

Although study authors said their examinations offered insights into the evolution of Neanderthals, none of the skulls actually belonged to a Neanderthal. Instead, they belonged to a group of Neanderthal ancestors that the authors have yet to give an official label.

"I'll give you an answer in the next month," Arsuaga said when asked for a name.

Modern humans, or Homo sapiens, are not the descendants of Neanderthals, although scientists say that we did share a common ancestor. It was about 30,000 years ago that all other species of the Homo genus went extinct, leaving only us.

Physical features that some of the Sima de los Huesos skulls exhibited were large, low-hinged jaws that allowed the mouth to open very wide — features associated with Neanderthals.

Other skulls exhibited projecting front teeth, which study authors speculated might have occurred as an adaptation to the environment. Arsuaga told reporters that this dental feature may have helped ancient humans to use their mouths as a "third hand" to grasp things, such as pieces of meat.

Arsuaga and his colleagues wrote that the skull braincases were roughly similar in size — smaller than those of modern humans.

The Sima de los Huesos site is considered an extremely rich archeological site, but the reason so many skeletons are found there remains a mystery.

While it's been speculated that the collection was a burial site, or the scene of a natural disaster, or even a predator's lair, Arsuaga said researchers had ruled these possibilities out for a variety of reasons.

He said they were left with one very simple reason as to why so many bodies would be gathered at the bottom of a deep shaft in the earth.

"They were thrown ... or made to fall from the top of the shaft by other hominins," Arsuaga said. "This is the explanation we consider as the most possible."